Micro-electrical-mechanical systems (MEMS) have been incorporated into many systems, for various civilian and military applications. Many MEMS actuators use direct electrical, pneumatic, or fluidic actuation. These direct actuation means, however, require large, bulky modules, which can be difficult to integrate within micro-systems, such as batteries or power supplies. Photovoltaic cells are used for optical-to-electrical energy conversion. However, voltage outputs are typically low, and overall photovoltaic optical-to-electrical conversion efficiencies are typically very low (e.g., 10%, up to 22% for specific wavelengths, and over 40% for cooled, multi-junction, commercial research cells).
Electromagnetic power transfer via radio frequency (RF) energy has been used an alternative to wires, pneumatic lines, or other tethers to the system. But, these systems have shown low efficiency of RF power transfer due to the small-sized antennas which must be with micro-systems. Additionally, thermal or chemical activation mechanisms also have been proposed as alternatives, but these have not been found to be readily controlled in a practical manner.
Researchers have demonstrated direct optical-to-mechanical wireless actuation schemes. For example, some have used polymer/carbon nanotube (CNT) composites which exploit the absorption characteristics of CNTs to cause a conformal change and significant strain therein as a result of a thermal expansion coefficient mismatch. Polarized light has been used to interact with liquid crystal elastomeric films which exhibit localized cross-linking or other phase changes leading to mechanical shrinkage, and which can be reversed by irradiating with light of a different wavelength. Non-polarized light has also been shown to cause localized shrinkage of shape memory polymers, such as pre-stressed polystyrene, through patterning of an optically absorbing material. And selective laser ablation of indium-tin oxide films has been used to form interesting folded structures controlled by laser positioning and fluence.
However, each of these conventional examples of optical actuation may be characterized as requiring either high irradiance levels (e.g., >1 W/cm2), long actuation times (10's to 100's of seconds), bulk films and/or materials which are not readily amenable to lithographic patterning and micro-fabrication.